The ultimate objective of our research program is to increase understanding of the general mechanism of gene activation in terms of chromatin structure. It is our working hypothesis that the association of different major proteins with given loci (and perhaps the modification of associated proteins) will dictate chromatin structure, and that this conformation in turn will have a significant effect on the accessibility of loci to transcription. We propose to continue to focus on an investigation of the major nonhistone chromosomal proteins (NHC proteins) of Drosophila, studying in particular their patterns of in situ distribution on polytene chromosomes, using an immunofluorescent assay recently developed in this laboratory. NHC proteins for study will be isolated from chromatin both by chemical fractionation techniques and by techniques designed to exploit the biological associations of the proteins (binding to the DNA: histone complex, binding to RNA polymerase, etc.). Concurrently work is being undertaken to develop a reliable in vitro transcription assay using Drosophila nuclei and chromatin. Ultimately one hopes to propose a model of chromatin structure for the general active and inactive forms which can be tested both by confirming the distribution of the major protein components in vivo and by examining the transcription properties of such a complex in vitro.